Just some random thoughts: I think that the open-ended tag is useless for ordinary puzzles for the reasons given by Doorknob (hence my UP vote for his answer). However, I think it has (limited) use for puzzles like the laser puzzle, where the open-ended-ness is not given by the fact that a 'better' answer can be found, but that each answer creates a new puzzle.
But I do have a big problem with this tag: The laser puzzle is the single one puzzle where I find it appropriate, and I'm not sure we would like to invite more puzzles of that kind.
This is not in anyway a down-valuing of the laser puzzle itself (I was the first to pick it up to get it rolling.), but it seemed to be or become more a game than a puzzle, and I really think this might be the point where we draw the line between "good for (Puzzling) SE" and "not suitable for (Puzzling) SE" - simply because the very nature of it contradicts the way this site has been build.
Personally, I think we should kill the tag to avoid inviting these type of questions.
( I think the laser puzzle could have fit better as either a request to create the most-interesting/difficult puzzle with the tool, or as presenting one or two very interesting puzzles with it. Both would have given it a permanent touch with the possibility to "accept & close" it. (Not as in VTC but as in closed=finished).